This invention relates to methods and apparatus for the detection of foreign materials in food substances, especially the detection of bones in meat, and will be particularly described with respect to the detection of chicken bones in chicken meat.
There are many known situations in which foreign material may be present in food substances, and should be detected either so it can be removed or so that the food substance containing it may be rejected or discarded. One example of such application occurs when it is desired to provide food consisting of animal meat, free of bones, under circumstances where bones unavoidably and inadvertently may occasionally be present. A specific example with respect to which the invention will be particularly described hereinafter occurs in the preparation of chicken meat for use in making chicken soup. The chicken meat is originally processed in a manner intended to remove all of the bones or bone fragments, but some always remain and if permitted to become a part of the soup present a possibility of discomfort or even harm to a consumer of the soup.
Many systems have been proposed and utilized in the past for the detection of foreign material in food substances, where it will be understood that the term "foreign material" may include material indigenous to the food substance but no longer desired therein, such as seeds, pits or bones. These prior systems include those involving transmission of various types of radiation through the food substance so as to deduce, from the intensity of the radiations transmitted to the food substance, whether or not foreign matter is present. X-rays have been proposed for this purpose, the basic operation being somewhat similar to the X-raying of human patients to detect the condition of bone or the presence of "foreign matter" in the human body. Where the foreign body to be detected has an X-ray absorption much different than that of the food substance, and where detection is to be visual by a human observer, such techniques may have a reasonable probability of success, since the image of the X-rays on a phosphorescent plate will then typically reveal discernible differences in image brightness between the region corresponding to the foreign material and immediately surrounding material; even in such systems, when the X-ray absorption coefficient of the foreign material is not very different from that of the surrounding material and/or the thickness of the foreign material is not great, detection of the foreign material can become difficult, and in the limit, impossible. Thus if the foreign material is quite thin and has an X-ray absorption coefficient only moderately different from the surrounding material, the difference in the X-ray intensity transmitted through it may not be discernibly different from the intensity of X-rays transmitted through the surrounding material.
Where the foregoing sensing of the transmitted X-rays is to be done automatically rather than visually, and an output signal reliably indicative of the presence of the foreign material is to be produced automatically, the problems of accurate and reliable detection increase. One source of such problems is that the specimen of food substance may in general have a randomly-variable thickness in the direction traversed by the X-rays. An example of this occurs with random specimens of chicken meat which are to be examined for the presence of chicken bone. Because of these random variations in thickness, the intensities of the transmitted X-rays will in general vary markedly at different points in the specimen even though no bone is present. These variations may readily be nearly as great as, or even greater than, the variations produced by bone, particularly small fragments of bone, and thus may mask the bone and prevent its reliable detection. Even if this problem due to variable meat thickness is overcome, it is still desirable to obtain the greatest possible sensitivity of detection with the smallest possible number of false indications of foreign material.
It is therefore an object of the invention to provide a new and useful method and apparatus for the detection of foreign material in a food substance.
It is also an object to provide such method and apparatus which automatically, and with a high degree of reliability, produce output signals in response to the presence of such foreign material.
Another object is to provide such method and apparatus which are capable of satisfactory operation even though the food substance is of randomly-variable thickness, and even though the extent of X-ray absorption by the foreign material is relatively small.
A further object is to provide such method and apparatus which are adapted for use in detecting foreign material in a food substance as it moves along a conveyor.
A further object is to provide such method and apparatus which are especially adapted for the detection of bone in meat, for example chicken bone in chicken meat.